Wastewater collection systems generally include a plurality of underground pipelines or sewer lines which contain and convey wastewater from property connection lines to treatment facilities. Preventive maintenance is performed in order to keep those pipelines clear by regularly eliminating blockages. In some localities, a high majority of those blockages are caused by root intrusion. Roots can also fracture sewer lines, causing soil and ground water contamination. Sewer line blockage is also commonly caused by grease accumulation. When sewer lines are not kept clear, streets, homes, and businesses can be contaminated with raw sewage.
Currently, preventive maintenance is performed using rodders and/or high pressure cleaners (hereinafter referred to as HPCs). A rodder is preferably used to deal with root intrusion (though a rodder may be used to remove grease also). A rodder consists of a saw/blade attached to rod (metal cables) which are contained within a cage. The saw/blades and rods are fed out of the cage while spinning. The resulting motion cuts and dislodges roots and grease allowing the intrusions to move down the sewer line towards a treatment facility. An HPC is preferably used to remove coagulated grease and grit (particulate matter) from the sewer lines. The HPC pumps water at a high pressure through the sewer lines. This water displaces the grease and grit.
Current preventive maintenance methods vary amongst localities. In many cities, cleaning all sewer lines is required within, for example, a five to seven year time span. Generally, each sewer line segment is cleaned between consecutive manhole/clean-outs with a rodder or HPC. The basis for this inclusive coverage is a presupposition that there is no feasible method to reliably distinguish between those sewer lines requiring service and those sewer lines not requiring service. That is, wastewater departments are unable to determine from ground's surface, via examining wastewater flow through manholes, whether or not a problem does or will exist. Therefore, all sewer lines are cleaned. As might be expected, such inclusive coverage demands extravagant amounts of equipment, manpower and money.
Another popular sewer line maintenance method is known as the wastewater collection management system (WCMS). WCMS is used either separately or in conjunction with the method of cleaning all sewer lines. WCMS uses computers to log and track those locations where problems have occurred, wherein problem locations are assumed to cause eventual stoppages or repeated stoppages. Thus, based upon a database of known problem locations, sewer line maintenance is performed periodically on the problem locations for preventing stoppages from occurring/reoccurring. One problem with WCMS is that sewer lines must cause a problem before being added to the database, and hence a health hazard is permitted and preventive maintenance is not truly accomplished. Additionally, an address reporting a problem may be accidentally logged as the problem area versus the actual problem area be reported (the problem line thereafter being neglected). Still another problem is that sewer lines peripheral to the problem sewer line are serviced in conjunction with the problem sewer line which defeats accuracy and efficiency. WCMS also fails to address those sewer line blockages/problems that are not yet detectable, but at a future date may cause a serious problem. For example, root intrusion may not be detected presently, but may later cause a structural failure to the sewer line resulting in a collapse. While this process may take years, in the interim, a partially fractured line will allow raw sewage to contaminate nearby soil and ground water.
Sewer line maintenance is also performed, in some localities, based only upon reported problems, even though some reported problems are not actually related to the public sewer lines (and not the responsibility of the sewer line maintenance department). This reactionary sewer line maintenance fails to account for a cause and effect relationship between roots/grease and the resulting stoppages/line damage. Stated differently, this method fails to recognize a basic rule of hydrology--water always seeks it's own lowest level. The specific densities of differing liquids and gasses results in a separation such that the most dense will seek the bottom while the least dense will seek the top. While in a contained system, such as a collection system, water always acts the same. Application of this rule is fundamental to determining whether a sewer line problem exists.
For example, a homeowner calls the local public works department with a common complaint; when the commode is flushed, water comes up the shower or floor drain. The public works department sends an emergency crew to the location. Upon arrival, the crew opens the closest upstream manhole to see if water is backed up at the bottom of the manhole. If water is backed up, a partial or complete obstruction exists in the public line and is the cause of the caller's problem. However, if the bottom of the manhole is lower than the lowest drain of the caller's property and no water is backed up at the bottom of the manhole, the problem is not caused by an obstruction in the main line. This is a false alarm. There is nothing the crew can do to relieve the problem. In spite of this fact, they are required to clean the line. This method is costly and yields nothing more than chance interception of roots or grease.
Accordingly it is desired to provide a preventive sewer line maintenance system that accurately identifies only those sewer lines highly likely to cause future blockages if not serviced, and to systematically service those sewer lines.